Thermo-responsive electric switch



THERMO-RESPONSIVE ELECTRIC SWITCH Edward H. Davis, deceased, late of Bristol, Ind., by Mary D. Davis Culler, administratrix, Elkhart, Ind.

Application October 5, 1953, Serial No. 384,159

2 Claims. (Cl. 200138) This invention relates to thermo-responsive electric switches, and more especially an improvement to my pending U. S. application for patent filed December 5, 1952, Serial Number 324,169, now Patent No. 2,709,732.

It is an object of the present invention to provide a thermo-responsive switch which will operate to close an electric circuit of an alarm system in response to a temperature rise of a predetermined degree, and which will reopen the circuit as the temperature drops below said predetermined point.

It is another object of the present invention to provide a switch of the above type which will snap closed responsive to a predetermined temperature rise, novel structural means being provided at the contact end of the moving lever to insure instant closing of the circuit.

Other objects of the present invention are to provide a thermo-responsive switch bearing the above objects in mind which is of simple construction, inexpensive to manufacture, has a minimum number of parts, is easy to use and efficient in operation.

For other objects and a better understanding of the invention reference may be had to the following detailed description taken in connection with the accompanying drawing, in which:

Figure 1 is a longitudinal sectional view of a thermoresponsive switch embodying the features of the present invention and shown .in an open position;

Fig. 2 is a side elevational view thereof and showing the switch in a closed position in dotted outline, and

Fig. 3 is a fragmentary perspective view of the switch parts.

Referring now to the figures, represents a supporting surface having an opening 11 over which is suitably secured a base member 12 of any suitable electrically non-conductive material, for example plastic.

A rectangular sheet of metal 13 of resilient bi-metal stock of any predetermined gauge is secured at one end to the base member 12 by means of a screw 14 and nut 15 serving as one terminal of the switch circuit. The strip 13 is provided intermediate its parallel longitudinal sides with a pair of longitudinal slots 16 (Fig. 3) equally spaced from said longitudinal sides extending from a point spaced from one end of strip 13 to a point spaced from the other end of said strip. A tongue 17 is thus provided. A cross cut or slot, connects the slot 16 at one end and through which passes the screw 14, spacing the end of tongue 17 from the strip 13 and causing it to flex in the manner shown in Fig. 1 and Fig. 3.

A spike 18 of conductive material is suitably secured to the other end of strip 13.

A contact strip 19 of resilient bi-metal stock and of substantially Z-shaped configuration is secured at one end to the top of base member 12 by means of a screw 20 and nut 21, the screw 20 serving as the other terminal of the switch circuit. The upper horizontal portion of the contact 19 is provided with an elongated slot 22 adapted to receive the spike 18 in the manner shown in Fig. 2.

States Patent 0 Preferably the strip 13 and contact 19 are formed from brass coated with silver.

Due to the flexing of the tongue 17 occasioned by the cross slot and screw 14, the spike 18 is extended upwardly and freely spaced from the contact 19 and slot 22 thereof (Fig. 1) upon the temperature rising a predetermined amount, the tongue 17 will snap into the reverse position (Fig. 2) and snapping the spike rapidly downwardly .into the slot 22 and closing the circuit. By receiving the spike within slot 22, an intimate contact is established between the two members which will cause the circuit through any coating that may have collected upon the spike 18 or contact 19, or both.

Bi-metal strips will bend in only one direction responsively to the heating thereof, and in the present case, the bend of tongue 17 is such as to cause the spike 18 to move rapidly downwardly onto the contact 19. This heat causes the tongue 17 to bend likewise and due to the fact that its inner end is spaced from the opposed end of the strip it is caused to buckle, gradually, to retain the ultimate shape of Fig. 2. As soon as the buckling is attained a given degree, at which it may be regarded in the light of having attained a dead center position, wherein the tension stress on the legs 23 is maximum and passes this position, the tongue 17 effects a more rapid downward movement of the spike 18 so that the electric circuit is closed as with a blow.

The present invention is preferably enclosed within a sheet metal casing 24 which may be of the sealed type or perforated to connect its interior with atmosphere.

The terminals 20 and 14, will, of course, be connected to a suitable electric signalling device or alarm, not shown.

While various changes may be made in the detail con struction, it shall be understood that such changes shall be within the spirit and scope of the present invention, as defined by the appended claims.

Having thus set forth and disclosed the nature of the invention, what is claimed is:

l. A therrno-responsive electric switch comprising a base member formed of non-conductive material, a switch lever composed of a strip of resilient bi-metal and having substantially parallel side edges and substantially parallel longitudinal slots parallel and spaced equi-dist-antly from said side edges, the portion of said strip lying between said slots being severed at one end, providing a tongue freely spaced from the rest of said strip, a metallic screw passed between the opposed end of said tongue and said strip through said base and constituting one terminal of an electric circuit and also operating to maintain said tongue .in spaced relation from said strip whereby to flex said tongue and a contact secured below the free end of said strip of resilient bi-metal, said contact at one end being secured to said base member by means of a second metallic screw constituting a second terminal of an electric circuit, said contact strip being of substantially Z- shaped configuration and provided with an elongated slot at the top portion thereof, said strip at the free end thereof having a pointed contact adapted to enter said elongated slot due to buckling of said tongue under a predetermined rise .in temperature.

2. A theme-responsive switch according to claim 1, including a sheet metal housing enclosing said strip and contact and secured at its lower edges to the edge of said base member.

References Cited in the file of this patent UNITED STATES PATENTS 2,286,053 Bletz June 9, 1942 2,429,812 Hausler Oct, 28, 1947 2,466,165 Fernandez-Castro Apr. 5, 1949 2,615,108 Lee Oct. 21, 1952 

